This section provides background information related to the present disclosure which is not necessarily prior art.
As plug-in hybrid electric vehicles (PHEV) and battery electric vehicles (BEV) grow in popularity, additional focus is being placed on making such vehicles more energy efficient. One area of focus is in regard to the energy used to heat and cool the passenger cabin of the vehicle.
For cooling, a typical vapor compression cycle based system, similar to that found on modern vehicles, is usually implemented. Such air-conditioning systems may include sub-cool condensers and internal heat exchangers to improve system efficiency and reduce the energy used to cool the passenger cabin.
Heating, however, can be a bit of a challenge. In particular, in a PHEV there is little to no wasted heat generated from an internal combustion engine to heat the passenger cabin, and a BEV has no internal combustion engine. Current techniques to overcome such issues may incorporate an electric heating element to heat the passenger cabin. For instance, a heater to heat the air directly or a heater used to heat water which is used to heat the cabin can be used. The problem with such design is that in the heating mode a PTC heater coefficient of performance (COP) cannot exceed 1. This means that if 5 kW of power is applied, 5 kW of heating can be achieved.
Alternatively, a heat pump system could also be used to heat the passenger cabin. With a heat pump system, a COP greater than 1 can be achieved in the heating mode, thereby saving energy. The heat pump system also utilizes the compressor and many other components that are already needed for the vehicle air-conditioning system. However, in a heat pump system, the outside heat exchanger is a condenser in the cooling mode and an evaporator in the heating mode. Therefore, the sub-cool section of the condenser is typically removed because it creates too much of a pressure drop in the heating mode. As a result, the efficiency of a sub-cool condenser during the cooling may not be realized.